Type annotations are optional and for people who do use them, they provide at least 2 substantial benefits: 1. Better code documentation. Based on my experienc

Type annotations are optional and for people who do use them, they provide at least 2 substantial benefits: 1. Better code documentation. Based on my experience with Python, reading someone else's code (or even my own code after a while) is harder than e.g. C or Java code because types do provide useful information. When reading Python function in isolation I often wander: is the argument to a function a list? a dictionary? a string? Knowing that makes a big difference when reading a code and when I don't know that it's hard to figure that out because you have to trace the whole control flow to that function. This is especially important in large projects where you can't keep all the code in your head and how to read small parts of it. 2. Tools can tell you about errors. Part of the Dart project are lint-like tools that check annotations and notify you about mistakes. If you e.g. annotate a function as taking integer but you pass string to it, a tool can tell you about such mistake. This is what statically typed compilers always do and, again, it's especially important on large projects where you're only responsible for part of the code. Dart doesn't force you to use type annotations but you can choose to use it in your project and get less bugs by using Dart code lint tool.